Belonoperca pylei is described from five specimens collected at depths of 68–122m from Rarotonga, Cook Islands. It differs from all other known diploprionin serranids in having IX, 10 dorsal-fin rays, III, 7 anal-fin rays, and a color pattern composed primarily of yellow and organge pigments. Cladistic analysis of epinepheline morphology supports monophyly of the diploprionin generaBelonoperca andDiploprion and suggests thatBelonoperca is the sister group ofDiploprion plus the monotypicAulacocephalus.